Optical switches, which are switching elements based on photons rather than electrons, are finding increased applications. In one example, optical switches are employed in conjunction with optical fibers in communication networks. In other cases, optical switching elements are being evaluated for use in ultra high speed computers since photons travel significantly faster than electrons, can travel in free space and can cross paths without interference.
Typical fiber-optic switches are relatively bulky, operate at low switching speeds, have limited lifetime switching cycles, and can access only a very limited number of channels. Examples of such fiber-optic switches are discussed with respect to FIGS. 1 and 2 below.
A class of optical media, particularly crystals, exhibits nonlinear behavior. The class includes materials such as Beta Barium Borate (BBO), Lanthanum Borate (LaB), Lithium Triborate (LBO), Nd:YAIBO.sub.3, Terbium and Erbium Borate, and Potassium Niobate.
Frequency doubling is an example of such nonlinear behavior. Frequency doubling is a specific example of what is known as the sum-frequency generation process, and occurs when an incident radiation of frequency v, on propagating through some crystalline materials, emerges as radiation consisting of a mixture of two frequencies, the original frequency v and a new frequency 2v.
The inverse of the aforementioned sum-frequency process is the optical parametric process, wherein incident radiation having a frequency v, on propagating through a nonlinear medium is converted into two lower frequency (higher wavelength) waves, which are of essentially variable frequency.
The parametric behavior of materials has been shown to be useful in creating optical logic gates. U.S. Pat. No. 4,405,869, entitled OPTICAL PARAMETRONS, shows an optical parametric logic gate. The parametric logic gate includes an optical resonant cavity having nonlinear optical characteristics, such that the cavity will generate a subharmonic output signal having a frequency f when supplied with a pump frequency 2f. The subharmonic output signal may have one of two possible phases which differ by .pi. radians and correspond to binary 1 and 0 respectively. A bias signal having a frequency f is supplied to the resonant cavity. Optical input signals are summed with the bias signal to produce a resultant seed input signal having one of two phases. The phase of the seed input signal is imparted to the phase of the output subharmonic. The type of logical operation which the parametron performs can be controlled by adjusting the power of the bias signal. Input and output interfaces for the optical parametron are also disclosed.
Another behavioral characteristic of nonlinear optical media is the ability of the material to change its refractive index in the presence of a strong electromagnetic field. In this manner, the angle of light passing therethrough can be modified according to the strength and direction of the field, albeit within a limited range of angles. This effect is a piezoelectric type effect, and is analogous to the magnetorestrictive effect observed in other materials and employed for micropositioning.